Method and apparatus for eliminating the effects of frequency offsets in a digital communication system

• US 8,363,757 B1
• Filed: 10/12/1999
• Issued: 01/29/2013
• Est. Priority Date: 10/12/1999
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Meng, Teresa H., Su, David, Zargari, Masoud
• Primary Examiner(s): Puente, Eva
• Application Number:
  US09/416,098
• Time in Patent Office: 4,858 Days
• Field of Search: 375/344, 375/140, 375/147, 375/150, 375/219, 375/229, 375/232, 375/326, 375/355, 375/373, 375/316, 375/358, 375/371, 375/260, 375/343, 375/376, 375/364, 370/342, 370/335, 370/465, 370/206, 370/347, 370/509, 370/210, 370/310, 370/252, 455/69, 455/500, 708/490
• US Class Current: 375/344
• CPC Class Codes: H03J 7/04 where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
• CPC Class Codes: H04B 1/38 Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
• CPC Class Codes: H04L 2027/0022 using the carrier of the associated receiver of a transceiver
• CPC Class Codes: H04L 27/0014 Carrier regulation of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657
• CPC Class Codes: H04L 27/148 using filters, including PLL-type filters
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop

Abstract

The present invention aims at eliminating the effects of frequency offsets between two transceivers by adjusting frequencies used during transmission. In this invention, methods for correcting the carrier frequency and the sampling frequency during transmission are provided, including both digital and analog implementations of such methods. The receiver determines the relative frequency offset between the transmitter and the receiver, and uses this information to correct this offset when the receiver transmits its data to the original transmitter in the return path, so that the signal received by the original transmitter is in sampling and carrier frequency lock with the original transmitter'"'"'s local frequency reference.

Claims

1. A device in a communication system, the communication system using one of OFDM, NBFDM, DMT, FDMA and TDMA, the communication system including a plurality of remote transceiver units and a central transceiver unit disposed remotely from the plurality of remote transceiver units, the plurality of remote transceiver units operable to communicate in a continuous bi-directional manner for direct exchange of information with the central transceiver unit, the device for providing that each of the plurality of remote transceiver units communicate with the central transceiver unit using a common frequency, the device comprising:

means for detecting, responsive to a continuous comparison of received and detected signals in each of the remote transceiver units, a comparative offset between common frequency references used locally by the remote transceiver units and the common frequency used by the central transceiver unit in at least one first signal transmitted between the central and the remote transceiver units, wherein the common frequency reference is a carrier frequency in a first remote transceiver unit and a sampling frequency in a second remote transceiver unit;

means for adjusting the common frequency reference in each of the remote transceiver units in accordance with the offset in at least one second signal to be transmitted between the remote and central transceiver units to correct for an error in the common frequency reference, so that effects of the offset in each of the remote transceiver units will be substantially reduced in preemptive manner, the second signal being in substantial frequency lock with the common frequency.

2. A device according to claim 1, wherein the means for detecting in the first remote transceiver unit includes means for performing a correlation on a digital representation of the first signal so as to lock onto the offset in the carrier frequency.

3. A device according to claim 1, wherein the means for adjusting in the first remote transceiver unit includes means for digitally shifting data in frequency in accordance with the carrier frequency and the offset corresponding thereto.

4. A device according to claim 1, wherein the means for detecting in the first remote transceiver unit includes means for locking onto the offset in the carrier frequency and for producing an output signal corresponding thereto.

5. A device according to claim 4, wherein the means for adjusting in the first remote transceiver unit includes means for variably adjusting a reference frequency output by a crystal oscillator in accordance with the output signal.

6. A method used in a communication system, the communication system using one of OFDM, NBFDM, DMT, FDMA and TDMA, wherein the communication system comprises a plurality of remote transceiver units operable to communicate in a continuous bi-directional manner for direct exchange of information with a central transceiver unit disposed remotely from the plurality of remote transceiver units, and wherein each of the plurality of remote transceiver units operates to communicate with the central transceiver unit using a common frequency, the method comprising:

detecting, responsive to a continuous comparison of received and detected signals in each of the remote transceiver units, a comparative offset between common frequency references used locally by the remote transceiver units and the common frequency used by the central transceiver unit in at least a first signal transmitted between the central and the remote transceiver units, wherein the common frequency reference is a carrier frequency in a first remote transceiver unit and a sampling frequency in a second remote transceiver unit; and

,

adjusting the common frequency reference in each of the remote transceiver units in accordance with the offset in at least one second signal to be transmitted between the remote and the central transceiver units to correct for an error in the common frequency reference, so that effects of the offset in each of the remote transceiver units will be substantially reduced in preemptive manner, the second signal being in substantial frequency lock with the common frequency.

7. A method according to claim 6, wherein the step of detecting for the first remote transceiver unit includes performing a correlation on a digital representation of the first signal so as to lock onto the offset in the carrier frequency.

8. A method according to claim 6, wherein the step of adjusting for the first remote transceiver unit includes digitally shifting data in frequency in accordance with the carrier frequency and the offset corresponding thereto.

9. A method according to claim 6, wherein the step of detecting for the first remote transceiver unit includes locking onto the offset in the carrier frequency and producing an output signal corresponding thereto.

10. A method according to claim 9, wherein the step of adjusting for the first remote transceiver unit includes variably adjusting a reference frequency output by a crystal oscillator in accordance with the output signal.

11. A device usable in any of a plurality of remote transceiver units, the remote transceiver units operating to communicate with a central transceiver unit using a common frequency, the central transceiver unit being disposed remotely from the plurality of remote transceiver units, the device comprising:

a frequency lock loop in a first remote transceiver unit and a delay lock loop in a second remote transceiver unit, the frequency and delay lock loops coupled to receive digital representations of at least one first signal transmitted by the central transceiver unit, the frequency and delay lock loops being respectively adapted to detect comparative carrier and sampling frequency offsets in the first signal and to produce offset information indicative of offsets between common frequency references locally used at the remote transceiver units and the common frequency used at the central transceiver unit; and

a frequency shift block in the first remote transceiver unit and a timing acquisition unit in the second remote transceiver unit, the frequency shift block and the timing acquisition unit coupled to receive the offset information and digital data to be transmitted and each to generate at least one second signal to be received by the central transceiver unit, the frequency shift block and the timing acquisition unit being respectively adapted to digitally shift and sample the digital data in frequency in accordance with the common frequency references and the carrier and the sampling frequency offsets corresponding thereto to correct for errors in the common frequency references, so that effects of the carrier and the sampling frequency offsets will be substantially reduced in preemptive manner for continuous wireless bi-directional communication between the remote and the central transceiver units for direct exchange of information.

12. A device usable in any of a plurality of remote transceiver units, the plurality of remote transceiver units to communicate with a central transceiver unit using a common frequency, the central transceiver unit being disposed remotely from the plurality of remote transceiver units, the device comprising:

a frequency lock loop in a first remote transceiver unit and a delay lock loop in a second remote transceiver unit, the frequency and delay lock loops coupled to receive digital representations of at least one first signal transmitted by the central transceiver unit, the frequency and delay lock loops being respectively adapted to detect comparative carrier and sampling frequency offsets in the first signal and to produce analog offset signals indicative of offsets between common frequency references locally used at the remote transceiver units and the common frequency used at the central transceiver unit;

a crystal oscillator in the first remote transceiver unit that supplies a reference frequency for modulating at least one second signal substantially locked with the common frequency; and

a variably adjustable device coupled to receive the analog offset signals, the variably adjustable device being respectively adapted to adjust the reference frequency of the crystal oscillator and a sampling clock of an analog-to-digital converter in accordance with the analog offset signals to correct for errors in the common frequency references, so that effects of the carrier and the sampling frequency offsets in the second signal to be perceived by the central transceiver unit will be substantially reduced in preemptive manner for continuous wireless bi-directional communication between the remote and the central transceiver units for direct exchange of information.

13. A device usable in a communication system, the communication system using one of OFDM, NBFDM, DMT, FDMA and TDMA, the communication system including a plurality of remote transceiver units operable to communicate in a continuous bi-directional manner for direct exchange of information with a central transceiver unit using a common frequency, the central transceiver unit being disposed remotely from the plurality of remote transceiver units, the device comprising:

means for detecting, responsive to a continuous comparison of received and detected signals in each of the remote transceiver units, a comparative offset between common frequency references used locally by said remote transceiver units and the common frequency used by the central transceiver unit in at least one first signal transmitted between the central and the remote transceiver units, wherein the common frequency reference is a carrier frequency in a first remote transceiver unit and a sampling frequency in a second remote transceiver unit;

means for communicating information corresponding to the offsets from the central transceiver unit to the first and second remote transceiver units; and

means for adjusting the common frequency references in the first and the second remote transceiver units in accordance with the offsets in at least one second signal to be transmitted between the first or second remote transceiver unit and the central transceiver unit to correct for errors in the common frequency reference, so that effects of the offsets will be substantially reduced in preemptive manner, the second signal being in substantial frequency lock with the common frequency.

14. A device in a communication system, the communication system using one of OFDM, NBFDM, DMT, FDMA and TDMA, the communication system including a plurality of remote transceiver units and a central transceiver unit disposed remotely from the plurality of remote transceiver units, the plurality of remote transceiver units operable to communicate in continuous bi-directional manner for direct exchange of information with the central transceiver unit, the device for providing that each of the plurality of remote transceiver units communicate with the central transceiver unit using a common frequency, the device comprising:

means for detecting, responsive to a continuous comparison of received and detected signals in each of the remote transceiver units, a comparative offset between common frequency references used locally by the remote transceiver units and the common frequency used by the central transceiver unit in at least one first signal transmitted between the central and the remote transceiver units, wherein the common frequency reference is a carrier frequency in a first remote transceiver unit and a sampling frequency in a second remote transceiver unit;

means for communicating information corresponding to the offsets from the central transceiver unit to the first and second remote transceiver units; and

means for adjusting the common frequency reference in each of the first and the second remote transceiver units in accordance with the offsets in at least one second signal to be transmitted between the remote and the central transceiver units to correct for errors in the common frequency references, so that effects of the offsets will be substantially reduced in preemptive manner, the second signal being in substantial frequency lock with the common frequency.